Factor B deficiency

Gene Information


HUGO name: BF


  • B-factor, properdin
  • Complement factor B precursor (EC
  • C3/C5 convertase
  • Properdin factor B
  • Glycine-rich beta glycoprotein
  • PBF2


Reference sequences

Chromosomal location


Protein Information


Protein function:

Factor B which is part of the alternate pathway of the complement system is cleaved by Factor D into 2 fragments: Ba and Bb. Bb, a serine protease, then combines with complement factor 3b to generate the C3 or C5 convertase. It has also been implicated in proliferation and differentiation of preactivated B lymphocytes, rapid spreading of peripheral blood monocytes, stimulation of lymphocyte blastogenesis and lysis of erythrocytes. Ba inhibits the proliferation of preactivated B lymphocytes.

Catalytic activity:

Cleaves C3 in the alpha-chain to yield C3a and C3b. Cleaves C5 in the alpha-chain to yield C5a and C5b. Both cleavages take place at the C-terminal of an Arginine residue.




Factor B is a Major Histocompatibility Complex Class-III protein.


Two major variants, F and S, and 2 minor variants, as well as at least 14 very rare variants, have been identified.


Expression pattern for human

Tissue Expression (%) Clones
uterus, pooled 15.47 52:15533
liver 8.34 47:26031
ovary, tumor tissue 8.22 2:1125
gall bladder 7.59 4:2435
nasopharynx 7.15 1:646
ovary, pooled 7.12 9:5846
hepatocellular carcinoma 6.82 21:14226
colonic mucosa with ulcerative colitus 3.79 1:1218
placenta human 8 week 3.44 3:4035
corresponding non cancerous liver tissue 2.99 9:13909